there are a lot of chemicals

A process area of a refinery, chemical plant or mining operation is referred to in the context of "battery limits". On a drawing, the battery limits is the area of interest.

You can run a deep cycle battery completely dead without damaging the battery. They are designed to be run down.

"Battery limits" in general simply outlines the limits of the work to be done by the engineer. If a refinery asks an engineer to carry out some work on the refinery, the battery limits need to be defined in order to determine what the engineer is responsible for and what he is not responsible for.

In the case of a refinery, for example, the battery limits might include sizing and costing a new heat exchanger. It could include the cost of utilities, installation, electrical needs, maintenance. Outside the battery limits might be how the utilities are supplied, how this heat exchanger is going to be delivered, who is going to build the exchanger etc.

Not long, but its not the apple that limits the life it is the amount of metal electrode surface available that the electrolyte in the apple can corrode that limits the life. Once the metal corrosion stops the battery is dead.